1. Field of the Invention
The present invention relates to improved methods and polymer compositions wherein degradation due to ultraviolet radiation is attenuated.
2. Description of the Prior Art
Metal oxide particles, e.g., titanium dioxide and zinc oxide particles, have heretofore been dispersed in polymer substrates for the purpose of minimizing ultraviolet radiation degradation of the substrates. The metal oxide particles either scatter or absorb harmful ultraviolet radiation thereby reducing damage to the polymer substrate. An example of a plastic product which has included titanium dioxide particles is polyvinyl chloride siding used in the construction or renovation of buildings and homes.
While the above described metal oxide particles dispersed in polymer substrates have functioned to reduce ultraviolet radiation degradation, the particles have generally been relatively large, i.e., approximately 0.2 micrometer in diameter and larger, and consequently they have not achieved maximum attenuation of the damaging effects of ultraviolet radiation.
Another desirable property of particles used for reducing ultraviolet radiation degradation is low opacity in the visible portion of the spectrum. This property is required so that the particles do not mask colored pigments which are added to paints and plastics. If the particles used for reducing ultraviolet radiation have such low opacity, lower quantities of the expensive colored pigments used in colored products or less expensive colored pigments with low tinting strengths can be used. As stated above, the metal oxide particles used heretofore have generally been relatively large and have not provided the minimum opacity possible.
By the present invention improved methods and polymer compositions containing ultraviolet attenuating particles are provided whereby ultraviolet radiation degradation is reduced to a minimum and relatively low particle opacity in the visible part of the spectrum is attained.